This invention is directed to reducing the size and current consumption of a battery-operated hearing aid, and in particular to utilizing field-effect MOS transistors to synthesize the circuitry of a hearing aid.
Heretofore, the circuits in a hearing aid, and in particular the amplifier thereof have been formed with bi-polar transistors operating in class A amplification mode, the respective bi-polar transistors being formed on a printed circuit board. One characteristic of class A transistor operation is that output current flows at all times and thereby rapidly exhausts the battery life. Many hearing aids presently on the market require the button-shaped battery utilized to energize same to be replaced every three days. Additionally, forming the amplifier circuit on a printed circuit board requires leads for coupling the amplification circuitry to the microphone and loudspeaker, which clearly lessens the reliability of the hearing aid and introduces noise into the signals amplified thereby.